Capacitor Calculator

A capacitor is a two-terminal electrical component that stores energy in an electric field between two conducting plates separated by a dielectric. Capacitance C is measured in farads (F) and relates charge Q to voltage V: Q = C x V.

Energy stored E = 0.5 x C x V squared, in joules when C is in farads and V in volts. A 100 microfarad cap at 12 V stores 0.5 x 1e-4 x 144 = 0.0072 J = 7.2 mJ.

Capacitors are the opposite of resistors. In series, total capacitance shrinks: 1 / C_total = sum of 1 / C_i. In parallel, capacitance adds: C_total = sum of C_i. Two 10 uF caps in series act like 5 uF; in parallel they act like 20 uF.

The RC time constant tau = R x C is the time for a charging cap to reach about 63.2 percent of supply voltage, or for a discharging cap to fall to about 36.8 percent. After 5 tau, the cap is within 0.7 percent of its final state and treated as fully charged or discharged.

The suffix letter is the SI prefix. Common values: F (farads), mF (millifarads, 1e-3 F), uF or microfarads (1e-6 F), nF (nanofarads, 1e-9 F), pF (picofarads, 1e-12 F). 47uF means 47 microfarads or 47 x 10^-6 farads.